Recent developments in microwave semiconductor devices have included the use of silicon bipolar transistors as amplifiers in place of traveling wave tubes for high frequency communications systems and radar. As dimensions become smaller, base resistance and emitter injection efficiency considerations limit the speed of bipolar transistors. Field effect transistors (FETs) however, do not have such limitations and can achieve higher powers at higher operating frequencies. One known type of FET structure is the planar or epitaxial type having source and drain electrodes on a common surface layer separated by a groove containing a gate or control electrode, with current flow parallel to the common surface. A second type is the vertical structure in which source and drain are positioned in different vertical layers with current flow perpendicular to that epitaxial surface. The gate electrode is also in a groove between the source and drain. Both types include an insulator or Shottky barrier to the flow of current interposed between the gate and drain which provides a diode type characteristic. Examples of each of the FET structures are found in U.S. Pat. No. 3,861,024 which relates to a planar configuration and U.S. Pat. No. 3,851,379 which describes a vertical metal oxide silicon device. The vertical structure provides several advantages including greater packing density, low thermal resistance, low output conductance with increased output power, less interface and spacing problems to enable attainment of high electron mobility and gain, carrier concentration can be tailored along the path of electron flow to increase breakdown voltage and maximum power, and very short gates can be used for mm wave applications. It is also known that gallium arsenide has superior semiconducting properties as compared with silicon. These include an electron mobility five times higher and a peak velocity twice that of silicon.